Electric valve circuit



Feb 7, 1939- w. F. WESTE'NDORP ELECTRIC VALVE CIRCUIT'` Filed Nov. 13, 1956 l V I Inventor: WiHem Ff Westendorpl b9 iff/M5 Patented Feb. 7, 1939 UNITED STATES PATENT OFFICE ELECTRIC VALVE CIRCUIT tion of New York Application November 13, 1936, Serial No. 110,654

11 Claims.

My invention relates to electric valve circuits for controlling electron discharge devices and more particularly to electric valve circuits for energizing and controlling electron discharge devices of the radiation type.

Heretofore there have been numerous circuits for impressing across electrodes of electron discharge devices suitable voltages to control the energy output of the electron discharge devices. In these applications, it has become evident that it is important that these control and energization circuits be capable of providing voltages which are easily and precisely controllable in magnitude to permit satisfactory control of the energy output of the electron discharge devices. Particularly in connection with the control and energization of electron discharge devices of the radiation type, such as X-ray tubes, it is highly desirable in many instances to provide easily controllable circuits for impressing across the electrodes of the devices voltages of relatively large magnitude without involving the use of eX- pensive and complicated apparatus. Furthermore, in circuits for energizing and controlling X-ray tubes, it is advantageous to suppress the inverse voltage to reduce the insulation requirements of the X-ray tubes and the insulation requirements of the associated equipment,

It is an object of my invention to provide a new and improved electric valve circuit.

It is another object of my invention to provide a new and improved electric valve circuit for controlling electron discharge devices.

It is a further object of my invention to provide a new and improved electric valve circuit for energizing and controlling electron discharge devices oi the radiation type such as X-ray tubes.

In accordance with the illustrated embodiment of my invention, an electron discharge device such as an X-ray tube is controlled and energized by an electric valve circuit which impresses across the anode and cathode of the X-ray tube a periodic voltage having positive portions substantially greater in magnitude than the negative portions. An inductive device, such as an induction coil, is connected to impress these relatively large voltages across the electrodes ci the X-ray tube, and the inductive device is energized from an alternating current circuit through an electric valve means of the type employing an ionizable medium and having a control member for rendering the electric valve means conductive. In order to effect the generation of high voltages across the secondary Winding of the inductive device by interrupting the current conducted to (Cl. Z50-100) the inductive device from the alternating current source through the electric valve means, there is provided a capacitance and a second electric valve means which are connected in series relation across the first-mentioned electric valve means. The capacitance is charged from any suitable source oi alternating current previous to rendering the first-mentioned electric valve means nonconductive when the second-mentioned electric valve means is rendered conductive. In order to conserve power, I provide an oscillatory circuit including an inductive element connected in series relation with a unidirectional conductive device, restoring to the capacitance the polarity which existed prior to the time the current was commutated from the first-mentioned electric valve means to the second-mentioned electric valve means. Due to the interruption of the current through the induction coil and due to the discharge of the capacitance through the secondmentioned electric valve means and through the induction coil, I provide a periodic voltage having a positive portion of relatively greater magnitude than the negative portion, soy that the voltage impressed across the cathode and the anode of the X-ray tube is characterized by having a useful portion which is substantially greater than the inverse portion. There are also provided means ior controlling the conductivity of the various electric valve means in order to control the magnitude oi the voltage impressed across the anode and the cathode of the X-ray tube and to eiect thereby control of the radiant energy output of the X-ray tube.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Fig. 1 of the accompanying drawing diagrammatically shows an embodiment of my invention as applied to a circuit for controlling the energization oi an X-ray tube; and Fig. 2 represents certain operating characteristics of the embodiment of my invention shown in Fig. 1.

In Fig. l of the accompanying drawing, I have diagrammatically shown my invention as applied to an electric valve circuit for controlling the energization of an electron discharge device which may be ci the radiation type such as an X-ray tube The Y-ray tube l is provided with a cathode 2 and an anode 3 which may be grounded through a connection 4, if so desired. For the purpose of energizing the cathode 2, I have chosen to represent a source of current as comprising a battery which supplies current to the cathode 2 through a resistance 6. In order to impress voltages across the electrodes of the X-ray tube I, that is, in order to impress between the cathode 2 and the anode 3, voltages of relatively large value, I employ a suitab-le inductive device such as an induction coil I having a primary Winding 8 and a secondary Winding 9. The terminals of the secondary winding 9 are connected across the cathode 2 and the anode 3 of X-ray tube I. As a means for controlling the energization of the induction coil 'I to effect energization and de-energization of the induction coil and hence to induce relatively large voltages in the secondary Winding 9, I provide an electric valve means Iil preferably of the type employing an ionizable medium, such as a gas or a vapor, and which is connected in series relation with the primary Winding 3 of the inductioncoil l and a suitable source of current 'such as a source of alternating current II. The electric valve means I8 is provided with an anode I2, a cathode I3 and a control member I II. The source of alternating current I I may be derived from any suitable source of alternating current I5 through a suitable transformer I6 to effect any desired voltage transformation. The energization of a primary Winding of the transformer IB may be controlled by employing an adjustable resistance II and a switch I8.

In order to render the electric valve means IIJ conductive at a predetermined time during positive half cycles of the voltage impressed across the anode I2 and the cathode I3 by th-e source I I, I provide a control or excitation circuit I9 Which may be energized from any suitable source of alternating current 2li. The source of alternating current 2t is preferably of the same frequency as the source of alternating current I5, and Where convenient the excitation circuit I9 may be energized from the alternating current circuit I5. The excitation circuit I 9 comprises a transformer ZI which is energized from the alternating current circuit 20 through any conventional phase shifting device, such as the rotary phase shifter 22, to impress on the control member I4 of electric valve means I8 an alternating voltage variable in phase relative to th-e voltage impressed on the associated anode I2. Any suitable source of negative biasing potential, such as a battery 23, impresses on the control member I4 of electric valve means I@ a negative biasing potential, and a current limiting resistance 24 is connected in series relation with the secondary winding of transformer 2| and the control member III.

A serially-connected capacitance 25 and an electric valve means 25 are connected across the anode I2 and the cathode I3 of electric valve means I!) to control an electrical condition of the anode-cathode circuit thereof to render the electric valve means I8 nonconductive and to thereby effect interruption of the current supplied to the primary Winding 8 of induction coil 'I from the source of alternating current II. Electric valve means 2E is preferably of the type employing an ionizable medium and is provided With an anode 21, a cathode 28, and a control member 29. The conductivity of the electric valve means 26 is controlled by means of an excitation circuit 38 which is energized from the alternating current circuit 25 through any suitable phase shifting arrangement such as the rotary phase shifter 3 I. Potentials of peaked Wave form are impressed on control member 29 of electric valve means 26 by any suitable means such as a peaking transformer 32 which is designed to provide an alternating potential of peaked wave form in order to precisely and accurately control the conductivity of electric valve means 26. Although I have chosen to show a peaking transformer as providing this voltage of peaked Wave form, it should be understood that I may employ any other conventional means for providing an impulse of voltage accurately determinable in phase relationship in order to control the conductivity of electric valve means 26. A battery 33 is employed to impress on the control member 29 a suitable negative biasing potential and a current limiting resistance 34 is connected in series relation With a secondary Winding of peaking transformer 32 and the control member 29.

An oscillatory circuit comprising a unidirectional conducting device 35 and an inductive element such as a secondary Winding 31 of a transformer 26 are connected in series relation and connected across the capacitance 25 to provide a discharge path for the capacitance 25 after current has been commutated from the electric valve means II) to the electric valve means 26. The unidirectional conducting device 35, by virtue of its unidirectional conducting characteristics, permits only one-half cycle of oscillatory discharge of the capacitance 25 so that the polarity of the capacitance 25 is restored to its initial charged condition. The transformer 36 may be energized from the alternating current circuit I5 or it may be charged from any suitable source of alternating current correlated in frequency and phase displacement in order to obtain the proper charging of the capacitance 25 relative to the operation of the electric valve means Il] and 2B. In addition to the charge reversing function described above, the transformer 36 serves to initiate the periodic operation of the circuit by establishing an initial positive charge on the righthand plate of capacitance 25. A resistance 38 is connected in series relation with the source I5 and a primary Winding of transformer 36 to control the voltage impressed on the primary Winding and hence to control the charge established on capacitance 25.

The operation of the embodiment of my invention diagrammatically shown in Fig. l will be explained by considering the electric valve circuit when it is operating to impress across the cathode 2 and the anode 3 of X-ray tube I suitable voltages so that the X-ray tube operates to produce an X-ray or Rntgen radiation. The transformer I6 will be energized from the alternating current circuit I5 upon closing the switch I8 so that there appears at the source I I an alternating voltage. Referring to the curves of Fig. 2, the voltage of source I I may be represented by curves A. If the electric valve means IIJ is rendered conductive by the excitation circuit I9 at substantially the beginning of each positive half cycle of voltage of the alternating current circuit I5, the primary winding 8 of the induction coil 1 will be energized from the source II through the electric valve means Il] and the current which ovvs through the primary Winding 8 may be represented by curve B. The capacitance 25 during this portion of the positive half cycle, as designated by curve C, Will be energized so that the right-hand plate of this capacitance is charged positively relative to the left-hand plate. If, at a time corresponding to the line a, the electric valve means 26 is rendered conductive by the excitation circuit 30, the current will be transferred or commutated from the electric valve means l0 to the electric Valve means 25 by virtue of the capacitance 25 and the electric valve means 26. Since the right-hand plate of the capacitance 25 has been charged positively relative to the left-hand plate, when the electric valve means 26 is rendered conductive there will be impressed across the anode I2 and the cathode i3 of electric valve means I a transient voltage Which renders the anode l2 negative relative to the cathode i3. The voltage appearing across the anode l2 and the cathode !3 of electric valve means I0 may be represented by the curve D and at the time corresponding to the time a at which the electric valve means 25 is rendered conductive, it will be noted that the anode l2 is negative in polarity relative to the cathode i3 causing deionization of electric Valve means Hl. Since the voltage impressed on control member lll of electric valve means le is negative at this time, the electric valve means li! will be maintained nonconductive for the remainder of the cycle after the time b. During the interval a-b, it will be noted that the current through the primary winding 3 of the induction coil 1 continues to rise due to the fact that the transient discharge of the capacitance 25 through electric valve means 26 tends to increase this current. However, during the interval b-c the current through the primary Winding 8 of induction coil l is rapidly decreased and nally interrupted due to the fact that the left-hand plate of the capacitance 25 has become positive relative to the right-hand plate. During the portion of the cycle lying beyond the time corresponding to the line b, the capacitance 25 will discharge through the oscillatory circuit including the secondary winding 3l of transformer 35 and the unidirectional conducting device 35. Due to the fact that the device 35 will conduct current in only one direction, there Will be only one-half cycle of oscillatory discharge of the capacitance 25 so the polarity of the capacitance 25 will be returned to its initial condition of energization, that is, the right-hand plate of the capacitance 25 will be made positive relative to the left-hand plate. This phenomenon is occasioned by the fact that there is considerable inductance in the circuit including the secondary Winding 3l of transformer 35 and the unidirectional conducting device 35. In other words, the natural periodicity of the circuit including the capacitance 25, the secondary Winding 3l of transformer 35 and the unidirectional device 35 is substantially greater than the natural periodicity of the circuit including the capacitance 25, electric valve means 26, secondary Winding of transformer E55 and the primary Winding 8 of transformer l. By this corn relation of natural frequencies of these circuits. the charging and discharging of the capacitance 25 is controlled to effect the desired current interrupting function oi electric valve means lil and 25. In addition, the transformer 35 supplies additional energy to the circuit due to the periodic ycharging of capacitance 25 from circuit i5.

Referring to curve D, it will be noted that dur ing the time corresponding to the interval a-b the anode I2 of electric valve means il! will be rendered negative relative to the cathode I3 for a time equal to or greater than the deionization time of the electric valve means I9, and since the potential on control member ill is negative the electric valve means lil is rendered nonconductivo to effect interruption of the current through primary Winding 8 of induction coil l. By virtue of the fact that the potential impressed on control member 29 of electric valve means 26 is of peaked Wave form, and the electric valve means 25 becomes nonconducting at the time C, there will be no tendency for the circuit to be energized through the electric valve means 25. The curve E represents the voltage appearing across the terminals of primary Winding 8 of induction coil 1 and the curve F represents the voltage appearing across the terminals of the secondary winding 9 and hence the voltage which is impressed across the cathode E and the anode 3 of the X-ray tube l. t is to be noted that the useful portion of the curve F, that is, the portion of the voltage which renders the anode 3 positive relative to the cathode 2, is substantially greater in magnitude than the negative or inverse portion.

If it is desired to control the intensity of the radiation of the X-ray tube I, this control may be effected by controlling the voltage appearing across the terminals of the secondary Winding 9 of the induction coil l. This may ce accomplished by controlling or adjusting the phase relationship of the alternating voltage impressed on control member li of electric valve means lil by the excitation circuit l?. As the phase of the voltage impressed on the control member id is retarded beyond the beginning of the positive half cycle of alternating voltage of the source H, as represented by curve A, the voltage appearing across the terminals of the secondary Winding 9 and hence the intensity of the radiation of the X-ray tube E Will be decreased. On the other hand, control of the intensity of the radiation or the X-ray tube i may be effected by controlling the time during each positive half cycle of the alternating voltage of source i! at which the electric valve means 2G is rendered conductive. For example, as the phase oi the voltage impressed on control member 2S of electric valve means 2S is retarded from the beginning of the positive half cycle of voltage, as represented by curve A, to successive points lying beyond the beginning of the cycle, the voltage appearing across the terminals of secondary Winding Si of the induction coil l' will be increased to effect an increase in the intensity of the radiation of the X-ray tube i. It is to be understood that the control of the X-ray tube l may be effected by separate or conjoint control of the electric valve means it! and electric valve means 25.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made Without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In combination, an electron discharge device having electrodes, en inductive device for impressing voltages across electrodes of said electron discharge device, a source of current, means for tran., ting variable amounts of current to said inductive device from saidsource and including elect dering said electnc valve me is the current through said i vice, and means for varying the so .c said electric valve means to cause id el valve means to conduct variable amounts or" on conductive to current to vary the magnitude of the voltages imvalve 1r ns, means for ren- I pressed across the electrodes of said electron discharge device.

2. In combination, an X-ray tube having electrodes, an induction coil for impressing voltages Vacross electrodes of said X-ray tube, a source of alternating current, means for energizing said induction coil from said source of alternating current comprising an electric valve means of the type employing an ionizable medium and having an anode, a cathode and a control member, means for rendering said electric valve means conductive at a predetermined time during each positive half cycle of voltage of said alternating current source by impressing on said control member a periodic alternating voltage, means for eiecting interruption of the current through said induction coil comprising a capacitance and an electric valve means having an anode, a cathode and a control member, said capacitance and said secondmentioned electric valve means being connected in series relation across the anode and cathode of said first-mentioned electric valve means, means for energizing said control member of said second-mentioned electric valve means for rendering said electric valve means conductive at a predetermined time during each positive half cycle cf said alternating current source to eiect transfer of the current from said rst-Inentioned electric valve means to said second-mentioned electric valve means, and means comprising a serially-connected inductance and a unidirectional conducting device connected across said capacitance for permitting only one half cycle oscillatory discharge of said capacitance after said second-mentioned electric valve means is rendered nonconductive.

3. In combination, an electron discharge device having electrodes, an inductive device for impressing voltages across electrodes of said electron discharge device, a source of alternating current, means for conducting current through said inductive device comprising an electric valve means connected in series relation With said inductive device and said source of alternating current, means for effecting transfer of current from said electric valve means comprising a serially-connected capacitance and an electric valve means connected across said first-mentioned electric valve means, means comprising a unidirectional conducting device for charging said capacitance and for permitting only one half cycle of oscillatory discharge of said capacitance after current has been commutated from said firstmentioned electric valve means to said secondmentioned electric valve means to re-establish the polarity of said capacitance to the condition which obtains prior to the time said rst-mentioned electric valve means is rendered conductive, and means for varying the conductivity of said rst mentioned electric valve means to vary the voltage impressed across said electrodes of said electron discharge device.

4. In combination, an electron discharge device having electrodes, an inductive device for impressing across electrodes of said electron discharge device potentials of relatively large magnitude, a source of alternating current, an electric valve means for energizing said inductive device from said alternating current source, means for interrupting the current through said inductive device comprising a serially-connected capacitance and a second electric valve means connected across said rst-mentioned electric valve means, means for charging said capacitance and to eiect commutation of the current from said first-mentioned electric valve means to said second-mentioned electric valve means when said second-mentioned electric valve means is rendered conductive, said last-mentioned means comprising a unidirectional conducting device and an inductance for permitting only one-half cycle of oscillatory discharge of said capacitance after current has been commutated from said first-mentioned electric valve means to said second-mentioned electric valve means to render said second-mentioned electric valve means non-conductive and re-establish the polarity of said capacitance Which existed prior to the commutation of current from said first-mentioned electric valve means to said second-mentioned electric valve means, and means for varying the conductivity of said rst mentioned electric valve means to vary the voltage impressed across said electrodes of said electron discharge device 5. In combination, an electron discharge device including electrodes, an inductive device connected to electrodes of said discharge device, a source of alternating current, an electric valve means for energizing said inductive device from said source, means for controlling said electric valve means so that said inductive device impresses on said electrodes oi said electric discharge device a periodic alternating voltage having portions of one polarity substantially greater in magnitude than the portions of opposite polarity comprising a capacitance and electric valve means connected in series relation directly across said iirst-mentioned electric valve means to render nonconductive periodically said rst-mentioned electric valve means to interrupt the current through said inductive device, said second mentioned electric valve means having a control member for controlling the conductivity thereof, and means for energizing said control member.

6. In combination, an electron discharge device having electrodes, an inductive device for impressing across electrodes of said electron discharge device voltages having portions of one polarity of relatively greater magnitude than the portions of opposite polarity, a source of current, an electric valve means for energizing said inductive device from said source, means for deenergizing said inductive device by rendering said electric valve means nonconductive comprising a serially-connected capacitance and a second electric valve means connected across said iirst-mentioned electric valve means for effecting transfer of current from said iirst-mentioned electric valve means to said second electric valve means, said second electric valve means having a control member, and means for impressing on said control member a periodic voltage adjustable in phase position to control the magnitude of said voltages.

7. In combination, an electron discharge device, an inductive device for energizing said electron discharge device, a source of alternating current, an electric Valve means having an anode,

a cathode and a control member for controlling the energization of said inductive device from said source, means for interrupting the current through said electric valve means, and means for controlling the voltage impressed on said control member to vary the current conducted by said electric valve means tocontrol the voltage impressed on said electron discharge device by said inductive device.

8. In combination, an electron discharge device, an inductive device for energizing said electron discharge device, a source of alternating current, an electric valve means having an anode, a cathode, and a control member for controlling the energization of said inductive device from said source, means for interrupting the current through said electric valve means, and means for impressing on said control member a voltage variable in phase relative to the voltage of said source of alternating current for controlling the voltage impressed on said electron vdischarge device by said inductive device.

9. In combination, an electron discharge device, an inductive device for energizing said electron discharge device, a source of alternating current, an electric valve means for conducting current to said inductive device from said source, means for effecting commutation of current from said electric valve means comprising a seriallyconnected capacitance and a second electric valve means connected across said first-mentioned electric valve means and having an anode, a cathode, and a control member, and means for controlling said second-mentioned electric valve means to effect control of the voltage impressed across said electron discharge device comprising a source of alternating voltage variable in phase relative to the voltage ci said alternating current source.

10. In combination, an electron discharge device having electrodes, an inductive device for impressing voltages across electrodes of said electron discharge device, a source of alternating current, an electric valve means for supplying current to said inductive device from said source, means for rendering said electric valve means nonconductive comprising a serially-connected capacitance and a second electric valve means connected across said first-mentioned electric valve means, said second-mentioned electric valve means including an anode, a cathode, and a control member, and means comprising a source of alternating voltage of peaked wave form variable in phase for energizing said control member to render said second-mentioned electric valve means conductive at predetermined times during the positive half cycles oi voltage of said source to effect deenergization of said inductive device.

11. In combination, an electron discharge device having electrodes, an inductive device for impressing voltages across electrodes of said electron discharge device, a source of alternating current, an electric valve means for supplying current to said inductive device from said source, a second electric valve means for eiecting transfer of current from said rst-mentioned electric valve means tosaid second-mentioned electric valve means to interrupt the current supplied to said inductive device, and an oscillatory circuit arranged to render said inst-mentioned electric valve means and said second-mentioned electric valve means nonconductive after current has been commutated from said first-mentioned electric valve means to said second-mentioned electric valve means.

WILLEM F. WESTENDORP. 

